Concrete battery molds are known in the art and come in a variety of sizes, designs and configurations. Battery molds are used for vertical casting of concrete panels or other concrete elements. A common element of all concrete battery molds is that they include a plurality of movable vertical rectangular mold halves or leaves that either hang from top rails and/or are supported on the bottom by rails or casters or both. The mold halves are closed for filling with concrete and are spread apart for stripping the cured concrete from the mold. State of the art battery molds allow for casting multiple concrete elements, such as slabs or walls, at the same time on a relatively small foot print. Generally, battery molds are used in precast concrete plants. In order to shorten production time and increase production capacity, precast plants pour and strip molds on a relatively short schedule. To achieve such a fast turn around, concrete precast plants use relatively large amounts of portland cement in the concrete elements. The stresses associated with demolding and moving concrete elements around the concrete plant within a few hours of pouring typically requires concrete mixes that use 900 lbs/yd3 of portland cement. By using such relatively large amounts of cement, a relatively large amount of heat is generated, which allows the concrete to set and gain strength in a relatively short amount of time. By comparison, similar onsite cast-in-place concrete elements may only require 450 lbs/yd3 of portland cement.
To withstand the pressure of concrete, battery mold leaves typically are made of metal, such as steel. Such the battery mold frames, leaves, halves or leaflets are highly heat conductive. Since a plurality of these elements filled with concrete are pushed together in thermal contact with each other, the battery mold acts somewhat like a mass concrete pour. The sum of all concrete slabs contained in the battery molds are in direct contact with each other through the heat conductive battery mold parts. The heat of hydration from one panel multiplied by the number of panels will significantly increase the internal temperature of the concrete slabs. In order to keep the concrete from achieving an unsafe temperature, battery molds limit the number of slabs in direct thermal contact. Once the concrete elements are stripped from the battery mold, they are moved to a curing room where steam and heat is used to complete the concrete curing.
Therefore, the precast concrete mixes used in a typical precast plant and battery mold is relatively expensive. Concrete used in a precast plant typically does not use any supplementary cementitious material, such as fly ash or slag cement. In addition there are significant drawbacks associated with using relatively large amounts of portland cement in a concrete mix. Portland cement concrete achieves 90% of maximum strength under ideal curing conditions in approximately 28 days. The more portland cement that is used in a concrete mix, the more brittle the concrete becomes. Precast plants use substantial pretensioned reinforcement (cables) to address brittleness of the concrete. In addition, the more portland cement that is used in a concrete mix, the more calcium hydroxide is generated, which makes the concrete susceptible to sulfate attack. However concrete made with fly ash and other pozzolanic materials are denser, less permeable and more resistant to sulfate attack.
Just like any other types of molds and concrete forming systems, prior art battery molds are only used to form and cast concrete. Battery molds are not used to cure concrete. In U.S. Pat. Nos. 8,545,749; 8,626,941 and 8,555,584, applicant has discovered that concrete forms can accelerate concrete curing when retaining the heat of hydration within the concrete form. The curing of concrete needs two basic elements, heat and water, to fully hydrate the cementitious material. The curing of plastic concrete is an exothermic process. This heat is produced by the hydration of the portland cement, or other pozzolanic or cementitious materials, that make up the concrete. Initially, the hydration process produces a relatively large amount of heat. When retaining the heat of hydration within an insulated concrete form, less portland cement per cubic yard can be used in order to achieve the same results. Since a battery mold contains a plurality of concrete elements that can be formed in direct thermal contact with each other, as a part of the present invention the cumulative energy of the heat of hydration of all panels can be used to further accelerate concrete curing, provided the battery mold is insulated in accordance with the present invention to retain the heat of hydration.
Portland cement manufacture causes environmental impacts at all stages of the process. During manufacture, a metric ton of CO2 is released for every metric ton of portland cement made. Worldwide CO2 emissions from portland cement manufacture amount to about 5-7% of total CO2 emissions. The average energy input required to make one ton of portland cement is about 4.7 million Btu—the equivalent of about 418 pounds of coal. The production of portland cement is energy intensive, accounting for 2% of primary energy consumption globally. In 2010 the world production of hydraulic cement was 3,300 million tons.
Concrete can also be made with slag cement (“SC”) and fly ash (“FA”) but are not frequently used. Slag cement and fly ash generate relatively low amounts of heat of hydration, which result in extremely slow concrete setting time and strength gain. Slag cement and fly ash can be mixed with portland cement but industry practice in building construction limits use of slag cement and fly ash to no more than 30% replacement of portland cement and only during warm weather conditions. Concrete made with slag cement and fly ash may take up to 90 days to achieve 80-90% of maximum strength. Mass concrete structures use more slag cement and fly ash, replacing up to 80% of portland cement, as a means to reduce the heat of hydration to reduce cracking Slag cement and fly ash use less water to hydrate, may have finer particles than portland cement and produce concretes that achieve higher compressive and flexural strength. Such concrete is also less permeable, and, therefore, structures built with slag cement and fly ash have far longer service lives.
Slag cement is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Slag cement manufacture uses only 15% of the energy needed to make portland cement. Since slag cement is made from a waste materials; no virgin materials are required and the amount of landfill space otherwise used for disposal is reduced. For each metric ton of pig iron produced, approximately ⅓ metric ton of slag is produced. In 2009, worldwide pig iron production was 1.211 billion tons. There was an estimated 400 million tons of slag produced that could potentially be made into slag cement. However, only a relatively small percentage of slag is used to make slag cement in the USA.
Fly ash is a by-product of the combustion of pulverized coal in electric power generation plants. When pulverized coal is ignited in a combustion chamber, the carbon and volatile materials are burned off. However, some of the mineral impurities of clay, shale, feldspars, etc. are fused in suspension and carried out of the combustion chamber in the exhaust gases. As the exhaust gases cool, the fused materials solidify into spherical glassy particles called fly ash. The quantity of fly ash produced is growing along with the steady global increase in coal use. According to Obada Kayali, a civil engineer at the University of New South Wales Australian Defense Force Academy, only 9% of the 600 million tons of fly ash produced worldwide in 2000 was recycled and even smaller amount used in concrete; most of the rest is disposed of in landfills. Since fly ash is a waste product, no additional energy is required to make it.
Historically, concrete has also been made using natural cements and other pozzolanic materials, such as volcanic ash, certain type of reactive clays, rice husk ash, metakolin, silica fumes and others. Pozzolanic materials have a relatively low rate of hydration thereby producing significantly less heat of hydration. Therefore concrete made with pozzolanic materials are seldom, if ever, used with current state of the art battery molds.
More recently pozzolanic materials, such a fly ash and volcanic ash have been modified through a process of fracturing which produces what is called “energetically modified cement.” Such pozzolanic materials are typically of a generally spherical shape but can be fractured so that the round sphere particle is broken up into multiple particles with more surface contact area. The greater surface contact area creates a higher reactive particle, therefore increasing the hydration properties of the pozzolanic material.
The present invention is applicable to all battery mold designs. To provide the present invention, a battery mold is enclosed on the top, bottom and all four sides by insulating material. The insulating material has sufficient insulating properties to retain a significant amount of the heat of hydration produced by the curing concrete cast within the molds of the battery mold. By retaining the heat of hydration, the curing of the concrete is accelerated and also produces concrete having improved physical properties. A battery mold in accordance with the present invention can be made portable and set up at a construction site. Since the battery mold is insulated, it can also be use to accelerate concrete curing regardless of the ambient temperature, such as in cold weather.